Junichi Masuda, one of the developers at Gamefreak who make the Pokemon games,has revealed a lot of information regarding the mysterious N from Pokemon Black and White. These could be considered spoilers if you haven’t had a chance to play either games yet.

N’s real name is Natural Harmonia Gropius, with “N” coming from the term natural number.
With his high IQ, N exceeds humans.
A genius, N excels in math enough to be called a math wizard.
N is quick-witted and has extreme mood swings.
N can see the past and future of people.
According to Masuda, rumors have it that N was born from Pokémon; the parents are unknown.
N loves Pokémon but keeps his distance from humans.
N believes he’s perfect.
Always putting Pokémon first is N’s ideology.
Given how he is, he has been shunned by humans. In effect, he has a very strong connection with Pokémon.

Eh, I never liked N. He seemed too much like one of those RPG characters that's all crazy and stuff (blah blah blah, don't trust humans, blah blah blah, you're all the same, blah blah blah), and you (supposedly) feel bad for him. That's why